1. Field of the Invention
The present invention relates to fuel injectors for use with internal combustion engines. The injector is used for the timed injection of gaseous fuel and may be used with conventional crank based engines. However, the injector finds particular utility when used for direct injection of gaseous fuel into a two-stroke free-piston engine.
2. Description of the Prior Art
Both mechanical and electromagnetic fuel injection systems are widely used to introduce fuel into internal combustion engines.
Mechanical injection systems of the Diesel-type supply pressurized liquid fuel directly into the combustion chamber of the engine. In these systems both the force required to inject the fuel, and the injection timing is derived directly from the mechanical motion of the engine.
The electromagnetic solenoid-type injector is typically used for indirect injection of liquid fuel into the manifold of a spark ignition engine. Less frequently this type of injector is used to inject fuel directly into the cylinder of a spark ignition engine. With injection systems of this type a high pressure vane-type fuel pump may be used to supply pressurized liquid fuel to an electromagnetic solenoid actuated fluid valve. Frequently, the mass flow rate of air into the engine is monitored by a computerized control system and an appropriate fuel injector duration is computed. A current pulse of an appropriate duration and magnitude is supplied to the injector solenoid to open it, typically the metering valve closes under spring pressure. In operation, a magnetic solenoid assembly lifts a fuel metering valve off a seat permitting pressurized fuel to be introduced into the engine manifold. The mass of the solenoid assembly limits the rate at which the valve can open and accurate metering requires an open duration in the tens of milliseconds range. In the case of a gaseous fuel injector, the volume of fuel required to inject is hundreds of times greater and therefore would result in an even larger and heavier valve. Consequently, the moving elements of such injectors cannot be synchronized with high engine speed for most direct injection applications.
Although indirect or manifold injection systems must accurately meter the fuel, there is a relatively long time interval to inject the fuel and therefore the mass of the injector valve structures is not as critical to fuel delivery performance. Since there is no requirement that injector operation be synchronized directly to engine motion, such injection systems typically emulate carburation systems. Prior art solenoid injectors of the type described are particularly unsuited for the synchronized injection of gaseous fuel into a variable stroke free-piston engine.